diff --git a/module3/exo3/exercice_en.ipynb b/module3/exo3/exercice_en.ipynb
index fe56feab9bd28e0cf21abc14bd4f8f63e2487bde..ce976b7a8a4d243a852a08dbf12eec21736f69ef 100644
--- a/module3/exo3/exercice_en.ipynb
+++ b/module3/exo3/exercice_en.ipynb
@@ -4,11 +4,11 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Research reproductable: work in pairs\n",
+    "## Research reproductable: work in pairs\n",
     "\n",
-    "#### Subject 2: Purchasing power of English workers from the 16th to the 19th century\n",
+    "### Subject 2: Purchasing power of English workers from the 16th to the 19th century\n",
     "\n",
-    "William Playfair "
+    "This document focus on reproducing William Playfair's research. William Playfair was a Scottish engineer and political economist. He has conducted a research about the purchasing power of English workers, including the wheat price and average salaries from 1565 to 1821. The most innovative contribution of him is his method to present his data: by the histogram."
    ]
   },
   {
@@ -507,6 +507,71 @@
     "raw_data"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "##### Tips on data:\n",
+    "- Until our time, 1 pound sterling = 20 shillings, and 1 shilling = 12 pences.\n",
+    "- Wheat price is given in shillings per quarter, and 1 quarter = 15 British pounds = 6.8kg.\n",
+    "- Salaries is given in shillings per week."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "#### Mission 1: Reproduce Playfair's graph\n",
+    "\n",
+    "Playfair presented wheat price by bars, and salaries by a blue surface delimited by red curve. The two graphs are plotted in the same figure."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "#### Mission 2: Improvement of data visulization\n",
+    "\n",
+    "To improve his presentation, we use two vertical axes on the left and right respectively; and plot the two graphs ensemble."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "#### Mission 3: Highlight our key points\n",
+    "\n",
+    "We define purchasing power as the **quantity of wheat a worker can buy with a weekly salary**, which varies with time. "
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Think about another method to present the advancement of time, to prove that workers' purchasing power increasing with time."
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,